Putting it Together -- MAF

Land Shark lndshrk at xmission.com
Thu Feb 1 17:57:56 GMT 1996


At 09:34 AM 2/1/96 EST, you wrote:
>Ok Guys,
>
>Anyone out there want to take a stab at putting all these threads
>together for a EE candidate who's better with chips and code than dynos and
>and lambda values and summarize the approaches to calculate the fuel charge
>per intake cycle based on the various sensors (MAF vs MAP vs none), throttle
>position, charge air and engine temp, and the pros and cons of each?  It seems
>everyone has an opinion, and "you know what they say about opinions..."

 Well, here's the math if you have a MAF that produces an analog voltage as 
 a function of the airmass

 First find Q ...

 Q=f(Up/Uv) where Up/Uv is the ratio of the MAF output to reference voltages

 (Bosch meters are logarithmic/exponential)

 From Q, the speed of the engine (n, in rpms) and a CONSTANT (Ki)
 which quantifies the fuel injector flow rate we can calculate
 the LOAD SIGNAL (Tl) which is effectively the THEORETICAL (Lambda=1)
 injector open time for the currently inducted amount of air 
 per engine cycle or stroke (depending on whether we have a 
 batch, semi-sequential, or sequential EFI system).

          Q
 Tl = ----------
        n * Ki

 With Tl quantified, we now take into account the vagarities
 of the particular engine family and operating conditions by
 introducing multiplicative factors to correct the theoretical
 injector time to the ACTUAL time for injection (Ti) needed 
 at that instant. Finally an ADDITIVE factor (Tv) is added to
 compensate for the differing injector opening time under lower
 than nominal voltages.


 Ti = (Tl * [C,D,E...]) + Tv


 It is this signal (Ti) that is applied to the injectors

 Hope this helps, it's from a BOSCH primer I'm writing ...

 Jim




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